This epidemiologic study has two components. The first involves screening of commonly used medicinal drugs for possible carcinogenic effects. The drugs dispensed to 143,000 subscribers to the Kaiser Foundation Health Plan in the years 1969-1973 have been stored in computer records. These subjects are followed up through Health Plan Records and subsequent incidence of cancer (each site and all sites) is determined for users of the drugs to be screened. The second component involves testing of hypotheses generated by the above screening analyses by detailed case-control studies involving the subjects' complete medical records.